Cyclomedusa
| Cyclomedusa Temporal range: | |
|---|---|
 | |
| Two large and small specimens of Cyclomedusa | |
Scientific classification  | |
| Kingdom: | Animalia (?) |
| Genus: | †Cyclomedusa Sprigg, 1947 |
| Species: | †C. davidii |
| Binomial name | |
| †Cyclomedusa davidii Sprigg, 1947 | |
Cyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20 cm are known. The concentric disks are not necessarily circular, especially when adjacent individuals interfere with each other's growth. Many radial segment lines — somewhat pineapple-like — extend across the outer disks. A few specimens show what might be a stem extending from the center in some direction or other.
Cyclomedusa is widely distributed in Ediacaran strata. There have also been occasional reports of Cyclomedusa from older rocks, with some dating back as far as the Orosirian some 2.0 to 1.8 Ga,[1][2] although due to the great age of these fossils, they remain controversial in nature, with some researchers suggesting them to be microbial colonies,[3] or dubiofossils.[4] Cyclomedusa was originally thought to be a jellyfish[5] but some specimens seem to be distorted to accommodate adjacent specimens on the substrate, apparently indicating a benthic (bottom-dwelling) creature.[6] The markings do not match the musculature pattern of modern jellyfish. The fossils have been conjectured to represent a holdfast for some stalked form — possibly an octacorallian, or something else entirely.[7] Alternatively, it was thought that the described species actually represent different modes of preservation for one organism or that several different organisms have been grouped together under one name as a form taxon.
It is now suggested that Cyclomedusa was a microbial colony;[8] D. Grazhdankin reinterprets the concentric rings and radial structures as comparable to those seen in modern-day microbial colonies exposed to homogeneously distributed environmental conditions.
Cyclomedusa is known from Neoproterozoic beds in Ediacara (Australia), Finnmark (Norway), Charnwood Forest (England), Olenek (Russia), North China, Newfoundland, Northwest Canada, Podolia (Ukraine), the Ural Mountains (Russia), the White Sea (Russia), Sonora (Mexico), and Mato Grosso (Brazil).[9] It is regarded as a member of the Ediacaran biota— a group of somewhat obscure organisms that thrived just before most of the modern multicellular animal phyla appeared. Cyclomedusa has no known relatives.[10]
See also
References
- ↑ Rasmussen, Birger; Bengtson, Stefan; Fletcher, Ian R.; McNaughton, Neal J. (10 May 2002). "Discoidal Impressions and Trace-Like Fossils More Than 1200 Million Years Old". Science. 296 (5570): 1112–1115. doi:10.1126/science.1070166. PMID 12004128.
- ↑ Rasmussen, Birger; Fletcher, Ian R; Bengtson, Stefan; McNaughton, Neal J (August 2004). "SHRIMP U–Pb dating of diagenetic xenotime in the Stirling Range Formation, Western Australia: 1.8 billion year minimum age for the Stirling biota". Precambrian Research. 133 (3–4): 329–337. doi:10.1016/j.precamres.2004.05.008.
- ↑ Morris, Simon Conway (4 October 2002). "Ancient Animals or Something Else Entirely?". Science. 298 (5591): 57–58. doi:10.1126/science.298.5591.57c. PMID 12365437.
- ↑ Cruse, Theresa; Harris, Lyal B. (March 1994). "Ediacaran fossils from the Stirling Range Formation, Western Australia". Precambrian Research. 67 (1–2): 1–10. doi:10.1016/0301-9268(94)90002-7.
- ↑ Sprigg, Reg. C. (1947). "Early Cambrian (?) Jellyfishes from the Flinders Ranges, South Australia". Transactions of the Royal Society of South Australia, Incorporated. 71: 212–224.
- ↑ (University of California at Berkeley) Cyclomedusa
- ↑ (Queens University) "Disk-Form Fossils of Canada" Archived 5 February 2012 at the Wayback Machine. Adolf Seilacher, in a series of papers (1985-92) called into question the assignment of the Ediacaran organisms to Animalia.
- ↑ GRAZHDANKIN, D.; GERDES, G. (2007). "Ediacaran microbial colonies". Lethaia. 40 (3): 201–210. Bibcode:2007Letha..40..201G. doi:10.1111/j.1502-3931.2007.00025.x.
{{cite journal}}: CS1 maint: deprecated archival service (link) - ↑ Kerber, Bruno Becker; Rosa, Ana Lucia Zucatti da; Gabas, Sandra Garcia; Leme, Juliana de Moraes; Pacheco, Mírian Liza Alves Forancelli (1 September 2013). "O registro fossilífero de metazoários ediacaranos na América do Sul e suas implicações nos estudos sobre origem e complexificação da vida animal". Geologia USP. Série Científica. 13 (3): 51–64. doi:10.5327/Z1519-874X201300030006.
- ↑ The few Ediacaran biota that survived into the Cambrian are discussed by Conway Morris 1993 and Narbonne 1998. However, if Cyclomedusa was a microbial colony, related microbes may be extant.